Becoming good at anything, be it flying, playing the guitar, writing, cooking, painting...you name it, requires practice. The more often and more regular you practice, the more quickly your skills improve. Also, the more structured your approach to your practice, the more quickly you improve. Some improve faster than others, due to natural talent, others take longer. But none of this really matters. All that matters is that you put your butt in the plane and fly. Once a week, once a month, whatever. Will it take longer to get your ticket flying once per week? Yes. Will it cost more if you fly only once per week vs two or three times per week? Possibly. (Historically, it usually does, but again, there's that "natural talent" aspect.)
If once a week is what you can afford, then that's what it is. The end result is what matters. And if you try to fly more often than you can afford to fly, you might end up quitting.
Do what's right for you.
Of course, different skills required, but I'm a guitarist (45+ years playing) but with guitar it's been so long, my training changes over time. I find in almost all training though for me, changing up helps a lot.
Even now if I am working on a very difficult song on guitar, I sometimes play the same part for hours, over and over..,it's not boring. But I can put the guitar down, next evening start again. Play through the whole song, then specific parts. But here is the thing, sometimes I make much better headway practicing more often for shorter time periods. It's the getting in the mindset, also not "practicing" but from the first note trying to play for real...
I also when I was first learning always had a guitar handy, would pick it up now and then, play, put it down, or pick it up and play all evening, playing also noodling and experimenting. Hard to have a plane and instructor handy like that, plus weather.
With aikido, I found just showing up three nights a week, work through the bad days enjoy the good, and plenty of reviewing in my mind between training helped (I even had a log book, with notes. Read through occasionally but the exercise of writing it down helped more than rereading. On rereading later in training the point I had were obvious now). But there they kinda stressed, once a week is maintenance, and you lose a little, three times is progress.
There is an excellent book by an author that trained in aikido about mastery. I'm not at home now so can't recall the name, but he talked a lot about the process, you hit a plateau (or you THINK you have) but you are really still progressing, but you notice it like you hop up a level. With guitar or aikido or any new learning students almost always make it harder than it is. Focus on the wrong things.
But with those things too, you have more consistency in the environment. That all landings are different, weather, etc, means learning to learn and keep open I think. I'm so new at flying I get worn out after an hours practice, but man...I recall a lot the whole time until next flight. Or did, I'm finally able to continue flying now. Weather is so bad around here, I'm gonna have to take any and all flight time I can, but shooting for at least twice a week when weather gets better. I don't mind if it ends up being once a week for a while, but do want to build up endurance, and also work on nausea which has hit me a few times.